Attrition resistant zeolite catalysts for production of methylamines in fluidized bed reactors

ABSTRACT

This invention provides an attrition resistant catalyst composition and method for producing such composition. The catalyst is comprised of an acidic zeolite, rho or chabazite, and a particulate binder, kaolin, bentonite, alpha-alumina, or titania, which can be optionally modified by treatment with a compound containing Si, Al, P or B. This invention further provides a process for producing methylamines, preferably dimethylamine, comprising reacting methanol and/or dimethyl ether and ammonia in the presence of a catalytic amount of an attrition resistant catalyst of the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 08/169,933filed Jan. 11, 1994, now abandoned.

This invention relates to attrition resistant zeolite catalysts whichare particularly useful for the production of methylamines in fluidizedbed reactors.

BACKGROUND OF THE INVENTION

Zeolite catalysts, and especially zeolite rho catalysts and their use infixed bed reactors for conversion of methanol and ammonia todimethylamine are well known in the art. (U.S. Pat. No. 3,904,738, U.S.Pat. No. 4,683,334, U.S. Pat. No. 4,752,596, U.S. Pat. No. 4,814,503,and U.S. Pat. No. 4,806,689.) The present invention provides animprovement in these catalysts whereby they are blended with one or moremicroparticulate binders during formation, which renders the catalystparticles attrition resistant and therefore suitable for use influidized bed reactor processes. A particularly useful aspect of theinvention is the use of these attrition resistant catalysts in fluidizedbed reactors for the efficient and cost effective commercial productionof methylamine compounds.

Other examples of improved related catalysts are known in the art.Gladrow et al., (U.S. Pat. No. 3,609,103) disclose use of faujasite anda deagglomerated clay such as Georgia kaolin matrix with asilica-alumina cogel to form a cracking catalyst. The use of the clayphase increases the cracking activity, and thus is added as an activecomponent for the cracking chemistry. Elliott (U.S. Pat. No. 3,867,308)discloses a process for preparing hydrocarbon cracking catalysts using asilica sol by first adding mineral acid to adjust pH, and then addingclay and zeolitic components followed by spray drying. These zeolitesare typically X or Y zeolites. Increased attrition resistance andactivity of the catalyst, compared to the pure H⁺ form of the zeolite isdisclosed. The process and additive are chosen to increase the activityof the catalyst by adding active components to the formulation. Gladrow(U.S. Pat. No. 4,147,613, U.S. Pat. No. 4,151,119 and U.S. Pat. No.4,182,693) disclose a hydrocarbon conversion process utilizing catalystcomprising major amounts of silica and minor amounts of zirconia andalumina, bulk alumina and aluminosilicate zeolites. (3-16 wt percentzeolite, 50-85 wt percent inorganic oxide gel, mostly consisting ofsilica and a minor amount of zirconia and alumina, and 15 to 40 wtpercent of a porous absorbent, for instance bulk alumina.) The absorbantis in place to absorb heavy metals present in the petroleum crudes,which can deactivate the zeolite. Increased activity/selectivities forthese catalysts compared to a more conventional Y zeolite containingkaolin and a silica-alumina hydrogel is claimed. Lim et al. (U.S. Pat.No. 4,206,085) report an improved abrasion resistant zeolite, preparedfrom a faujasite type zeolite, hydrated alumina and ammoniumpolysilicate or silica sol and clay to form microspheres. The use ofball clay is present because the clay has pre-cracking activity which isimportant in the hydrocarbon chemistry.

Lim et al. (U.S. Pat. No. 4,325,845) describe a method for producingzeolite cracking catalysts using sodium silicate, derived from silicagel, in combination with clay to form catalysts of good attritionresistance. The authors eliminate the alumina from the formulation(pseudoboehmite), claiming it is a source of coking, or deactivation ofthe catalyst and sodium silicate is substituted for the alumina hydrate.The silicate is added to the ball clay and zeolite to form the finalcatalyst in order to enhance catalytic activity.

Scherzer (U.S. Pat. No. 4,987,110) claims an attrition resistantcracking catalyst using a molecular sieve (zeolite) having crackingactivity, a clay such as kaolin, a silica sol and aluminumchlorohydroxide. In contrast to the present catalysts, the claydisclosed by Scherzer would have significant activity in themethylamines chemistry. Velten et al. (WO 89/01362) claim variouszeolites (ZSM-5, ultra stable Y) formulates with binders prepared fromamorphous silica, alumina and zirconia, particularly those of colloidaldimensions. Binder formulations include colloidal silica, colloidalalumina, colloidal silica and acid dispersed alumina which may benoncolloidal or colloidal, colloidal silica and colloidal zirconia, ormixtures of these ingredients. Applicants have found that colloidalsilicas, aluminas and silica/alumina combinations do not give asatisfactorily attrition resistant rho zeolite at 50 weight percentbinder or greater.

SUMMARY OF THE INVENTION

The present invention provides an attrition resistant catalystcomposition comprising one or more acidic zeolites selected from rho orchabazite; said zeolite being uniformly admixed to a final weight % ofabout 25 to 75 with one or more particulate binders selected fromkaolin, bentonite, alpha-alumina, and titania; wherein said catalystcomposition is optionally modified by treatment with one or morecompounds containing elements selected from Si, Al, P and B, saidtreatment comprising depositing at least 0.05% by weight of the compoundonto the surface of the catalyst particles.

The present invention further provides a process for producing amethylamine compound, preferably dimethylamine, comprising reactingmethanol and/or dimethylether and ammonia, in amounts sufficient toprovide a carbon/nitrogen ratio from about 0.2 to about 2.5, and at atemperature from about 220° C. to about 450° C., in the presence of acatalytic amount of an attrition resistant catalyst compositioncomprising one or more acidic zeolites selected from rho and/orchabazite; said zeolite being uniformly admixed to a weight % of about25 to 75 with one or more particulate binders selected from kaolin,bentonite, alpha-alumina, and titania; wherein said catalyst compositionis optionally modified by treatment with one or more compoundscontaining elements selected from Si, Al, P and B, said treatmentcomprising depositing at least 0.05% by weight of the compound onto thesurface of the catalyst particles. Preferably, the above process is usedto produce dimethylamine in a fluidized bed reactor.

The present invention further provides a process for the production ofan attrition resistant catalyst composition comprising one or moreacidic zeolites selected from rho and/or chabazite, said zeolite beinguniformly admixed with one or more particulate binders selected fromkaolin, bentonite, alpha-alumina, and titania; wherein said catalystcomposition is optionally modified by treatment with one or morecompounds containing elements selected from Si, Al, P and B, saidtreatment comprising depositing at least 0.05% by weight of the compoundonto the catalyst composition,

said process comprising the steps of:

(a) blending one or more acidic zeolites selected from rho and/orchabazite with one or more particulate binders selected from kaolin,bentonite, alpha-alumina, and titania, at a ratio of from about 25 toabout 75 weight %;

(b) adding the blend to water to yield a slurry of about 20 to about 55wt percent solids;

(c) spray drying the slurry to form microspherical particles;

(d) calcining the particles at about 500° C. to about 750° C.; andoptionally;

(e) screening the calcined particles to produce a catalyst compositionhaving the desired median particle diameter (d₅₀).

DETAILED DESCRIPTION

The advantages of fluid bed catalytic processes over fixed bed processesare well recognized in the art. The advantages in fluid bed processesinclude improvement of temperature control because of better heattransfer and more efficient solids handling. Particularly in the case ofzeolite catalysts for methylamines synthesis, it is recognized thatprecise temperature control is important to maintain the activity of thecatalyst and eliminate the formation of hot spots which are known tooccur in fixed bed reactors. Additionally, if the catalyst losesactivity with time, it can easily be removed and replaced in a fluid bedreactor. A fixed bed reactor, however, requires the reactor system to beshut down for catalyst removal.

The activity, stability and durability of a catalyst in a fluidized bedcatalytic process depend on the inherent attrition resistance of thecatalyst particle. Most zeolites, as prepared, do not have the correctparticle size range for such a reactor. Hence, they must be formed inthe correct particle size range. Attrition by abrasion and/or fractureof the particles is a frequent problem in fluidized reactors, whichnecessitates the addition of a binder to the catalyst particles.Excessive particle attrition in these reactors is caused, for example,by particle-to-particle contact, abrasion with bed walls and bedinternals, as well as distributor jet impingement and abrasion incirculation conduits leading to and from the reactor bed. High particleattrition contributes to product contamination, catalyst loss, pluggingof down stream equipment, high filtration costs, and unstablefluidization behavior such as channeling, slugging or increasedentrainment of reactants. The deleterious effects of fluidized bedoperations can be exacerbated by high temperature conditions. Zeolitesby themselves cannot be formed in the correct particle size range withsufficient mechanical strength to be attrition resistant.

In addition to mechanical strength, particle shape can also have animpact on attrition. Spheroidal particles with smooth surfaces will havelower attrition losses than particles with irregular shapes and roughedges. By spheroidal we mean to include spherical and nearly sphericalparticles, so long as there are no irregular or sharp edges that wouldlikely cause attrition during handling or fluidization.

For a fluid bed methylamines process, a catalyst of high attritionresistance as well as sufficient activity/selectivity is necessary. Theuse of binders to impart attrition resistance however, introducesadditional entities which may have their own reactivities resulting inundesirable competing side reactions. For these reasons, priorliterature is not directly applicable in any particular catalyticprocess. Most previous disclosures in this art concern FCC (fluidcracking catalysts). For these systems, however, the binders are chosenfor their catalytic activity towards hydrocarbons. Since fluid crackingis also an acid catalyzed reaction, these FCC catalysts will haveundesirable activity on the methylamines reactants. This reactivity isdeleterious to the overall selectivity of the catalyst since themolecular sieving characteristic is not a feature of these binders.

Thus, in developing the attrition resistant catalysts of the inventionfor methylamine production in fluidized bed systems, applicants werefaced with many obstacles and constraints. Primarily, the goal was toselect the appropriate types and amounts of binders to blend with theappropriate zeolites whereby sufficient catalytic activity and attritionresistance of the catalyst particles was attained for use in commercialfluid bed reactors. Constraints included:

1) minimizing reactivity of the binder phase;

2) controlling the selectivity of the zeolite/binder in producingmethylamine compounds in the dimethyl form;

3) producing attrition resistant fluidizable material without excessiveheating in order to preserve the integrity of the zeolite.

The attrition resistant catalysts of the invention are either comprisedof acidic zeolites rho or chabazite. These and other zeolites can bedescribed as aluminosilicates characterized by a three-dimensionalframework structure occupied by ions and water molecules. Rho zeoliteand chabazite contain a common structural characteristic: pores orchannels within the zeolite framework, the largest of which are boundedby 8-membered rings of tetrahedral atoms. This structural characteristicis associated with catalytic selectivity for production of dimethylaminefrom methanol and ammonia; the catalyst possesses a geometric or shapeselectivity which permits the release of dimethylamine andmonomethylamine from the zeolite pores, but not trimethylamine.

Zeolite rho is a small-pore synthetic zeolite which can be described bythe formula

    (Na,Cs).sub.12 Al.sub.12 Si.sub.36 O.sub.96.44 H.sub.2 O.

The structure and synthesis of this synthetic zeolite are described byRobson et al., "Synthesis and Crystal Structure of Zeolite Rho--A NewZeolite Related to Linde Type A", Advances in Chemistry Series 121(American Chemical Society 1973), and Robson, U.S. Pat. No. 3,904,738,incorporated by reference herein. The cation species Na⁺ and Cs⁺ presentin rho zeolites can be exchanged with H⁺ or ammonium ions to prepare anacid or ammoniated form (NH₄ -rho) which is then converted to the acidform by calcination at elevated temperatures (ion exchange of ammoniumfor Na⁺ and Cs⁺ ions may be incomplete in any given experiment,typically leaving 0.5-1.0 Cs per unit cell; the product of this ionexchange is referred to as NH₄ -rho; similarly, deammoniation of NH₄-rho may not result in complete conversion of all NH₄ sites to H+ and/orother acid sites).

Chabazite, a mineral zeolite, has a structure consisting of identical,near-spherical "chabazite cages", each composed of two 6-rings at topand bottom, six 8-rings in rhombohedral positions, and six pairs ofadjacent 4-rings. Each cage is interconnected to six adjacent units bynear-planar, chair-shaped 8-rings. Chabazites can be characterized bythe formula:

    M.sub.a.sup.n Al.sub.12 Si.sub.24 O.sub.72.40 H.sub.2 O

In this formula, the product of a and n is 12, and M generally refers toCa, Mg, Na and K. As with rho zeolite, the cations can be exchanged forH⁺ or by conversion to an ammoniated form which can then be converted tothe acid form by calcination at elevated temperatures, generally rangingfrom 400 to 600° C.

Zeolites rho and chabazite are known to be useful as catalysts formethylamines synthesis in fixed bed reactors. See U.S. Pat. Nos.3,904,738, 4,683,334, 4,752,596, 4,814,503 and 4,806,689. The presentinvention encompasses such known methods of methylamines synthesis infixed bed reactors, as well as methylamines synthesis in fluidized bedreactors, wherein the catalyst is attrition resistant per the method ofthis invention, discussed below.

Thus, a process of the present invention comprises reacting methanoland/or dimethylether (DME) and ammonia, in amounts sufficient to providea carbon/nitrogen (C/N) ratio from about 0.2 to about 2.5, in thepresence of a catalytic amount of attrition resistant catalystcomposition, at a temperature from about 220° C. to about 450° C.Reaction pressures can be varied from 1-1000 psi (7-7000 kPa) with amethanol/DME space time of 0.01 to 80 hours. The resulting conversion ofmethanol and/or DME to methylamines is generally in excess of 85% (on amole basis).

The process variables to be monitored in practicing the process of thepresent invention include C/N ratio, temperature, pressure, andmethanol/DME space time. The latter variable is calculated as the massof catalyst divided by the mass flow rate of methanol and DME introducedto a process reactor (mass catalyst/mass methanol+DME fed per hour.)

Generally, if process temperatures are too low, low conversion ofreactants to dimethylamine and monomethylamine will result. Increases inprocess temperatures will ordinarily increase catalytic activity,however, if temperatures are excessively high, equilibrium conversionsand catalyst deactivation can occur. Preferably, reaction temperaturesare maintained between 270° C. and 350° C. more preferably 290° C. to330° C. with lower temperatures within the ranges essentially preferredin order to minimize catalyst deactivation. At relatively low pressures,products must be refrigerated to condense them for further purificationadding cost to the overall process. However, excessively high pressuresrequire costly thick-walled reaction vessels. Preferably, pressures aremaintained at 10-500 psi (70-3000 kPa). Short methanol/DME space timesresult in low conversions and tend to favor the production ofmonomethylamine. Long methanol space times may result either ininefficient use of catalyst or production of an equilibrium distributionof the products at very high methanol/DME conversions. Generally,methanol/DME space times of 0.01-80 hours are satisfactory, withmethanol/DME space times of 0.10-1.5 hours being preferred(corresponding to methanol/DME space velocities of 0.013-100 gmethanol+DME/g of catalyst/hour, preferably 0.67-10 g of methanol+DME/gof catalyst/hour).

The molar reactant ratio of methanol and/or dimethylether to ammonia,herein expressed as the C/N ratio (g atoms C/g atoms N), is critical tothe process of the present invention. As the C/N ratio is decreased,production of monomethylamine is increased. As the C/N ratio isincreased, production of trimethylamine increases. Catalyst deactivationis also greater at high C/N ratios. Accordingly, for best results, C/Nratios should be maintained between 0.2 and 2.5, preferably from 0.5 to2.2 and most preferably 1 to 2.0 in conducting the process of thepresent invention.

The efficiency of the process of the invention is measured by overallconversion of methanol and/or DME to methylamines, and by selectivity ofdimethylamine production. For example, if methanol is used as the solereactant, overall conversion is determined by comparison of the amount(in moles) of methanol in the product mixture, which is considered to beunconverted, to the amount in the reactant feed. Thus, overallconversion in percent is given by: ##EQU1## Selectivity of methanol tomonomethylamine (MMA) in percent, is given by: ##EQU2## Similarly,selectivity of methanol to trimethylamine (TMA), in percent, is givenby: ##EQU3## Finally, selectivity to dimethylamine (DMA) is calculatedby analysis of product composition. Thus, selectivity to DMA, inpercent, is provided by the following expression: ##EQU4##

For efficient operation, the catalyst must be selective at highconversion (87-98%) and a C/N ratio of 0.2-2.5, preferably 0.5-2.2, andmost preferably 1-2.0.

Comparison of selectivities for different samples should be made atsimilar conversions since selectivity varies with conversion. At lowconversions, MMA production is favored, at very high conversions, thereaction will approach an equilibrium distribution and thus result inincreased TMA production.

Because of its high activity and shape selectivity for monomethylamineand dimethylamine, rho zeolite is preferred over chabazite.

The binders of the invention which are admixed with the zeolites may becomprised of one or more of the following metal oxides, most of whichare neutral or mildly acidic for use in methylamine synthesis and whichhave sufficient mechanical properties to confer attrition resistance inmicrospherical catalysts compositions: alpha-alumina, titania, bentoniteand kaolin.

Submicron alpha alumina is most preferred because of its hardness andcatalytic inertness. Bentonite is preferred because of its exceptionalbinding efficiency.

In order to form the catalyst in microspheres, a spray drying process isemployed, the first step of which is the formation of an aqueous slurrycontaining the binder and the zeolite catalyst. In some cases, the pH ofthis slurry can be important (pH can be adjusted by the addition of anappropriate acid, such as nitric acid). For instance, a range in pH ofthe composition from <2 to >9 will not significantly change theattrition characteristics of the composition for the bentonite ortitania binders. However, for the alpha alumina system, a pH≦about 2(about 1.8) is preferred. In addition, for the alpha alumina systems, itis desirable to hold the slurry, with high speed stirring, for about 1-2hours prior to use.

The standing particle size of the binders range from 0.2 to 3micrometers. Alpha alumina is available from various suppliers in theform of powders with a median particle diameter (d₅₀) between about 0.2and 3 micrometers. In the case of Alcoa's A16 SC alpha alumina (AlcoaIndustrial Chemicals, Bauxite, Ariz.) a high yield of submicronparticles can be obtained by slurrying the powders in water anddecanting the fine fraction of particles. Bentonite is analuminosilicate clay consisting of submicron agglomerates of colloidalparticles. It can be obtained from various suppliers, one of which isSouthern Clay Products, Gonzales, Tex. as Gellwhite H--NF. TiO₂ can beobtained as a submicron powder from Degussa. Much of the TiO₂ used inthis study is a fumed titania, Degussa's P25 (Degussa, PigmentsDivision, Ridgefield Park, N.J.). The ultimate particle size of thebinder has an influence on the attrition resistance of the zeolitecomposites. For instance, <0.5 micron alpha alumina binders (with rhozeolite) imparts a lower attrition rate (by about 50%) than 0.5micrometer alumina. In addition, the crystallite size of the rho zeoliteshould be micron sized or lower for proper dispersion. Use of a highspeed mixer is preferred for proper dispersion of the aqueous slurryused for spray drying.

A preferred catalyst composition is formed using rho zeolite as thecatalyst component. In a typical preparation, it was found that thehydrogen form of rho zeolite (calcined) or the ammonium form(uncalcined) could be blended with the appropriate binders by slurryingboth components, zeolite and binder with water (water-based solution) tomake a 20-50 wt % solids.

The slurry is then spray dried to form the microspherical particles.Spray drying conditions are chosen to produce a particle ranging from 20to 150 microns. Some experimental parameters, such as slurryconcentration, atomization pressure and feed rate can affect theparticle size distribution and particle microstructure. These parameterswill also vary with the spray dryer configuration and nozzle type usedto prepare the material. Applicants used a 4.5 ft i.d. spray dryerfitted with a two fluid nozzle in a countercurrent, fountainconfiguration. Typical conditions include a feed rate of 160 ml/min.,inlet temperature of 376° C., and outlet temperatures of 160-170° C.

The spray dried powders are then calcined in air by heating at about600° C., and maintained at that temperature for 8 hours.

The calcined powder is screened to produce a catalyst in the correctparticle size distribution and to minimize particles less than 20microns in diameter. Typically, a distribution of particles ranging from20 to about 150 microns in diameter is produced. A median particlediameter (d₅₀) of 50 to 70 microns is usually obtained. The medianparticle diameter (d₅₀) is calculated based on median cumulative volume,assuming all particles are spherical. The median cumulative volume isdetermined from a gaussian distribution based on particle volume.

Additionally, to further enhance selectivity to methylamines, thecatalysts of the invention can be modified by treatment with one or morecompounds selected from the group consisting of silicon, aluminum,phosphorous, and boron, by depositing at least 0.05 weight percent ofthe element. Such deposition can be performed at various steps in thecatalyst preparation. For a detailed description of such modificationmethods, see U.S. Pat. Nos. 4,683,334 and 4,752,596.

Attrition measurements are performed using an attrition mill whichsimulates particle attrition near the gas spargers of a fluidized bed. Acatalyst charge is loaded into a column fitted with a single 0.016"perforation. Air flows through the perforation, fluidizes the catalystbed, and causes attrition. For most measurements, the constant air flowthrough the mill is calibrated to yield a linear velocity of 760 ft/sthrough the orifice; this compares to a typical velocity of 150 ft/s ina commercial fuel spargers. The attrition mill measurement acceleratesattrition by a factor of roughly thirty. A 24 hour attrition measurementis a reliable indicator of attrition in a commercial reactor. Attritedfines (i.e., those particles lower than 20 micrometers in diameter) arecollected in an overhead flask which is fitted with a porous thimble.Flask weight, recorded as a function of time, is used to calculateattrition. The determination of attrition is calculated as an attritionratio, AR: catalyst attrition divided by the attrition rate of a fluidcracking catalyst standard (FCC). The FCC standard is supplied byDavison Chemical, Baltimore Md. (SMR-5-5209-0293). This catalyst, whichcontains zeolite Y, is typical of the highly attrition resistantcatalysts used in FCC Catalytic Crackers for petroleum refining. As usedherein, for a catalyst to be considered attrition resistant, theattrition ratio (AR) should be less than or equal to about 3.

In all cases, in addition to the attrition resistance determined byweighing the fines collected in the flask, the contents of the bed areanalyzed by SEM (scanning electron microscopy) as well as for particlesize distribution (Coulter Counter or Microtrack techniques) to checkthat any fines that are produced are properly elutritated (disengaged)from the attrition mills. A catalyst is considered to be attritionresistant only if the weight of fine particles carried over to the flaskis acceptably low, and if the contents of the mill do not show anyappreciable quantities of fine particles (particles less than 20 micronsin diameter).

EXAMPLE 1 50% Rho/50% α-alumina

A catalyst composition was formulated using a 50/50 by weight mixture ofNH₄ -rho zeolite to alpha Al₂ O₃ by the following method.

To 10 gallons of deionized water, 50 g of concentrated HCl acid isadded. 6300 g of alpha alumina powder was added (over a period of about30 minutes) while maintaining the pH (pH=4) with the hydrochloric acid.This slurry was continuously stirred at high speeds for an additionalperiod of 30 minutes. It was then allowed to settle undisturbed forabout 4 days. Most of the mother liquor was then decanted off andconcentrated by evaporation (boiling, with stirring). This procedureseparated the larger alpha alumina particles from the smaller fineparticles. These alpha alumina particles (fines) are then submicron inparticle size.

In this example, the mother liquor was decanted off and concentrated toabout 50.3 wt % solids. 1590 g of this slurry was diluted with 521 gdeionized water. 800 grams of the ammonium form of rho zeolite was thenadded to this slurry (about 55 wt % solids at this point). Concentratednitric acid was then slowly added, over the course of about 1 hour, tobring the slurry to a stable pH of about 1.9 (about 540 g of nitric acidwas added). This was performed while mixing with a stirrer at a speed ofabout 800 rpm. The slurry was then allowed to sit (with stirring) foranother hour. This slurry was not allowed to settle before spray drying,because redispersion would be difficult. The composition of the slurryand the spray dried material contained approximately 50 wt % rho zeoliteand 50 wt % of the alpha alumina binder.

This slurry was then poured through a cheesecloth, to filter out anyvery large clumps of catalyst, and then pumped into a spray dryer. Thisspray dryer is a 4 ft diameter, 8 ft straight end electrically firedBowen Dryer. It can operate using a two fluid nozzle in counter currentmode or a rotary disk nozzle co-current. In these experiments, a twofluid nozzle was employed. Typical conditions include a feed rate of 160m/min, an inlet temperature of 376° C. to the dryer and outlettemperatures of 160-170° C.

Spray drying yields were typically 70%. This powder was then calcined inalumina trays to 600° C. for 8 hrs in flowing air. A slow temperatureramp (of about 2-5° C./min) was used. Following this procedure, thecatalyst was sieved on +100, -325 mesh screens prior to attritiontesting or reactor evaluations.

The catalyst was characterized by a variety of techniques. SEM (scanningelectron microscopy) was used to check the formation of the fluidizablemicrospheres. It was also employed to check the contents of theattrition mills, after an experiment, for any fine particles which maynot have elutriated. X-ray diffraction was used to established theintegrity of the rho zeolite. Catalysts were evaluated in fixed bedmicroreactors to check the catalyst activity and selectivity tomethylamines as described in Example 8, except where noted. This alsoapplies to examples cited below.

The results of catalyst attrition and activity testing are shown inTable 1 for all examples.

EXAMPLE 2 70% Rho Zeolite/30% Bentonite

A catalyst composition was formulated using a 70/30 by weight mixture ofNH₄ -Rho zeolite to bentonite clay by the same methods employed inExample 1, except for the following differences:

350 g of the ammonium form of rho was slurried with 150 g of bentoniteclay (Gellwhite H--NF, Southern Clay Products, Gonzales, Tex.) and 2000ml deionized water. In this example, the final pH was about 8, and thefinal wt % solids was 20. This slurry was spray dried and calcinedaccording to the procedure described in Example 1 to produce anattrition resistant catalyst. The approximate final composition is 70%weight rho zeolite/30% weight bentonite clay.

EXAMPLE 3 50% Chabazite/50% Alpha Alumina Catalyst

A catalyst was prepared in a similar fashion to that used in Example 1,with the following exceptions:

150 g of chabazite was mixed with 395 g of alumina alumina "fines"slurry (containing 38 wt % of alpha alumina) and 324 g of deionizedwater (35 wt % solids slurry). The pH of the water and the aluminaslurry was adjusted with concentrated nitric acid to a pH of 1.8. Themixture was vigorously stirred for at least 30 minutes prior to spraydrying. Other processing steps are similar to those of Example 1, exceptthat the activity testing was conducted at a reaction temperature of400° C.

EXAMPLE 4 50% Rho/50% TiO₂ pH=9.5

A catalyst was prepared in a manner similar to Example 1, with thefollowing exceptions:

150 g of rho zeolite was slurried with 150 g of titania (Degussa's P25,Degussa Pigments Division, Ridgefield Park, N.J.) in 1000 g of water.About 2.5 mL of concentrated ammonium hydroxide was added to bring thefinal pH to 9.5. The slurry was continuously stirred for about 30minutes prior to spray drying.

EXAMPLE 5 50% Rho/50% TiO₂ pH=1.8

A catalyst was prepared in a manner similar to Example 1, with thefollowing exceptions:

150 g of rho zeolite was slurried with 150 g of titania (Degussa's P25,Degussa Pigments Division, Ridgefield Park, N.J.) in 1000 g of water.Nitric acid was added to bring the final pH to 1.8. The slurry wascontinuously stirred for about 30 minutes prior to spray drying.

EXAMPLE 6 50% Rho/50% Kaolin

A catalyst was prepared in manner similar to Example 1, but with thefollowing exceptions:

150 g rho zeolite was mixed with 150 g of kaolin (Engelhard, Edison,N.J.) in 1000 ml of deionized water. The slurry was continuously stirredfor 30 minutes prior to spray drying.

EXAMPLE 7 30% Rho/70% Bentonite

A catalyst was prepared in manner similar to Example 1, but with thefollowing exceptions:

105 g of rho zeolite was slurried with 245 g of bentonite (GelwhiteH--NF, available from Southern Clay Products, Gonzales, Tex.) and 2300ml of deionized water to make a 13% slurry with pH=8.05. The materialwas then spray dried.

EXAMPLE 8 TEOS Treatment of 50% Rho/50% α-alumina

This example demonstrates the utility of tetraethylorthosilicate (TEOS)treatment of 50% rho zeolite/50% α-alumina catalyst to improvemethylamines selectivity:

500 g of a 50 wt % rho/50 wt % α-alumina catalyst from Example 1 wereslurried with 1500 ml of TEOS. The slurry was then filtered and dried atroom temperature, and then calcined for 3 hours at 500° C.

Approximately 2 grams of the catalyst that had been granulated to a 20to 40 mesh size fraction was placed in a stainless steel U-tube reactor,0.25 (0.64 cm) in diameter and 18 to 20 in (45.7 to 50.8 cm) in length.The reactor was heated to a reaction temperature of 300° C. in afluidized sand bath. A 1/1 molar mixture of liquid methanol and ammoniawas vaporized and then passed through the reactor into contact with thecatalyst at a pressure of 200 psig. The flow rate of the liquid feed wasvaried from 2 ml/hr to 16 ml/hr. The reactor effluent was continuouslyanalyzed by on-line gas chromatography for dimethyl ether, methanol,water and mono-, di-, and trimethylamine. The methanol conversions andmolar selectivities to the amines are listed in Table 1.

Selectivity to a given methylamine is calculated by analysis of productcomposition as follows:

For example, DMA Selectivity is given by: ##EQU5##

A procedure similar to that described in this example was used to testfor methylamines selectivity for the catalysts of other examples.

EXAMPLE 9 Fluidized Bed Testing

A catalyst consisting of TEOS treated 50% rho zeolite/50% alpha alumina(from Example 8) was tested in a fluidized bed reactor used formethylamines synthesis. The catalyst had a particle size distributionranging from 35 to 235 microns. The fluid bed reactor had an L/D of 16and L/D of 3 for the disengaging section, and was operated at atemperature of 323° C. and 300 psi. A 1/1 molar mixture of MeOH/NH₃ wasvaporized at 250° C. and passed at a rate of 497 g/hr through 489 g ofthe catalyst. The methanol conversion was 89.2%; the feed and productstreams were analyzed by on-line gas chromatography. Methylaminesselectivity results are shown in Table 1.

COMPARATIVE EXAMPLE A

A 50% zeolite rho with 50% silica (from colloidal source) catalyst showsthat silica is detrimental to attrition resistance.

A procedure similar to that described in Example 1 was used. 150 g rhozeolite was mixed with 374.7 g of colloidal silica (40 wt % solution,Ludox® AS-40, available from DuPont, Wilmington, Del., which wasacidified with Dowex® HCRW2 resin, available from Dow Chemical Company,Midland, Mich., to a pH=5.3) and 780 ml of water. The slurry was spraydried. This procedure produced a catalyst with attrition ratio, AR>20,which is therefore not attrition resistant.

COMPARATIVE EXAMPLE B

This example demonstrates that the addition of a silica from a colloidalsource does not increase the attrition resistance of a rho/bentonitesystem.

A procedure similar to that described in Example 1 was used. The silicasource was polysilicic acid, PSA, which was formed by deionizing sodiumsilicate with sulfonic acid resin, Dowex® HCRW2 (Dow Chemical Company,Midland, Mich.). For a complete description of the method to prepareaqueous PSA solutions, see U.S. Pat. No. 4,677,084. In this experiment,a 5 wt % SiO₂ solution was used. 105 g rho zeolite were mixed with 210 gbentonite (Gellwhite H--NF, Southern Clay Products, Gonzales, Tex.), and777.4 g of the PSA solution. Additionally, 25 ml H₃ PO₄ was added tomaintain a low pH for PSA stability. This method yield a catalyst have30% rho zeolite, 60% bentonite and 10% SiO₂, which was not attritionresistant, AR>5.

COMPARATIVE EXAMPLE C

A 50% alumina (from colloidal source) binder with 50% rho zeolite toshow non-attrition resistance.

A procedure similar to that described in Example 1 was used. 200 g ofthe ammonium form of rho zeolite, was mixed with 200 g of alumina (1000g of 20% by weight solution, Nyacol Products, Ashland, Md.) and anadditional 142 g of water, resulting in a slurry of about 35% solids byweight. The ph was adjusted with nitric acid to about 2.27. The mixturewas slurried for approximately an hour before spray drying.

This procedure produced a catalyst with AR>4, which is therefore notattrition resistant.

COMPARATIVE EXAMPLE D

A 25% silica/25% alumina (from colloidal sources) binder with 50% rhozeolite to show non-attrition resistance.

A procedure similar to that described in Example 1 was used. 200 g ofthe ammonium form of rho zeolite, was mixed with 150 g of colloidalalumina (750 g of 20% by weight solution, Nyacol Products, Ashland, Md.)and 150 g of silicon oxide (375 g of 40% by weight solution, Ludox®AS-40, available from DuPont, Wilmington, Del.), resulting in a slurryof about 35% solids by weight. The pH was adjusted with nitric acid toabout 2.4. The mixture was slurried for approximately an hour beforespray drying.

This procedure produced a catalyst with AR>8, which is therefore notattrition resistant.

COMPARATIVE EXAMPLE E

A comparative example with Y zeolite is described below. The catalystcomposition is 50 wt % Y zeolite/50 wt % alpha alumina (fines)

A procedure similar to that described in Example 1 was used. 125 g of Yzeolite (ultra stable Y, containing 7% rare earth oxide, DavisonChemical, Baltimore Md.: SMR 6-2558-0491) was added to an acidifiedslurry of alpha-alumina fines (125 g/0.228=548 g of slurry. Anadditional 42 g of deionized water was added to the slurry. The finalweight % solids in the slurry was 35%, and the slurry had beenacidified, prior to the addition of the zeolite, with nitric acid to apH of 1.9. The Y zeolite and alpha-alumina fines were held in the slurryfor about 15-30 minutes prior to spray drying. This procedure produced acatalyst with AR>4, which is therefore not attrition resistant.

COMPARATIVE EXAMPLE F

A comparative example of 50 wt % Na Mordenite 50 wt % alpha-aluminafines is described below.

369 g of a 38% solids slurry containing alpha-alumina fines (preparedaccording to the procedure described in Example 1) was used with 302 gof deionized water, acidified with nitric acid to a pH of 1.9. 140 g ofNa mordenite was then added to this slurry, which was held for about 30minutes prior to spray drying. This procedure produced a catalyst withAR>12, which is therefore not attrition resistant.

(Note: Mordenite has a channel-like pore structure consisting oftwelve-membered rings. The Si/Al ratio in this structure is 5/1, with anideal unit cell formula

    Na.sub.8 (AlO.sub.2).sub.8 SiO.sub.2).sub.40.4 H.sub.2 O.)

COMPARATIVE EXAMPLE G

A comparative example of 30 wt % NH₄ -Mordenite 70 wt % bentonite clayis described below.

75 g of the ammonium form of mordenite was slurried with 175 g ofbentonite (Englehard Products, Edison, N.J.) and 815 g of deionized H₂O. No adjustments to pH were made; the final pH of the slurry was 7.1.This mixture was spray dried and calcined and according to theprocedures described in Example 1 and was not attrition resistant.Scanning electron micrographs of the attrition mill contents, followinga 24 hour attrition experiment, showed a majority of particles werebelow 20 microns. This indicates high attrition rates in the catalystbed with poor elutriation of the fine particles (below 20 microns indiameter) into the overhead flask in the attrition mill. In addition,the catalyst bed did not fluidize properly after a short time in theattrition mill, which is most likely a result of the improper particlesize distribution that results from high attrition rates and poorelutriation of fine particles.

COMPARATIVE EXAMPLE H

A comparative example with Y zeolite (30 wt %) bentonite (70 wt %) isdescribed below.

The ammonium form of Y zeolite (75 g) was used in a slurry of 175 gbentonite (Englehard, Edison, N.J.), 815 g of deionized water (finalpH=6.5; 23.5 wt % solids). The material was calcined and treated as inthe above examples, and it was not attrition resistant.

Scanning electron micrographs showed that a significant amount ofparticles were below 20 microns. The catalyst bed did not fluidizeproperly after a short time in the attrition mill. Additionally, theparticle shape was not microspheroidal; the particles were agglomeratedinto irregular shapes, which also did not fluidize well, making it apoor fluid bed catalyst. (Ammonium exchanged Y zeolite (NH₄ --Y);Contains 21.4% Si, 9.56% Al, 0.18% Na; available from Linde Division ofUnion Carbide, N.Y., N.Y.)

                                      TABLE 1                                     __________________________________________________________________________    Attrition and Reactor Data                                                                    g recvrd/g std                                                                (approximate)                                                                        % MMA                                                                              % DMA                                                                              % TMA                                                        std = .05-1.0 g                                                                      90%  90%  90%                                          Ex.                                                                             % zeolite                                                                            % binder                                                                             (@ 24 hrs)                                                                           conv.                                                                              conv.                                                                              conv.                                        __________________________________________________________________________    1 50% rho                                                                              50% α-Al.sub.2 O.sub.3                                                         ˜1                                                                             32   59    9                                           2 70% rho                                                                              30% bentonite                                                                        ˜1                                                                             33   50   17                                           3 50% chabazite                                                                        50% α-Al.sub.2 O.sub.3                                                         ˜2                                                                             37   49   13                                           4 50% rho                                                                              50% TiO.sub.2                                                                        ˜1                                                                             32   55   13                                             pH = 9.41                                                                   5 50% rho                                                                              50% TiO.sub.2                                                                        ˜1                                                                             30   64    6                                             pH = 1.8                                                                    6 50% rho                                                                              50% kaolin                                                                           ˜1                                                                             30   58   11                                           7 30% rho                                                                              70% bentonite                                                                        ˜1-2                                                                           29   60   11                                           8 50% rho                                                                              50% α-Al.sub.2 O.sub.3                                                         ˜1                                                                             32   64    4                                             (TEOS treated)                                                              9 50% rho                                                                              50% α-Al.sub.2 O.sub.3                                                         ˜1                                                                             32   63    5                                             (TEOS treated;                                                                Fluidized Bed)                                                              __________________________________________________________________________

What is claimed is:
 1. A process for the production of an attrition resistant catalyst composition comprising the steps of:(a) blending one or more acidic zeolites selected from the group consisting of rho and chabazite with one or more particulate binders selected from the group consisting of kaolin, bentonite, alpha-alumina, and titania, at a ratio of from about 25 to about 75 weight %; (b) adding the blend to water to yield a slurry of about 10 to about 55 weight percent solids; (c) spray drying the slurry to form microspherical particles comprising a composite of zeolite and binder; and (d) calcining the particles at a temperature of about 500 to 750° C.
 2. The process of claim 1 further comprising depositing at least 0.05% by weight of one or more elements selected from Si, Al, P and B, onto the catalyst particles.
 3. The process of claim 1 wherein at step (c) the microspherical particles are formed to a diameter of about 20 to about 200 microns.
 4. The process of claim 1 wherein the calcined particles are screened to produce a catalyst composition having a median particle diameter (d₅₀) of from about 50 to about 70 microns.
 5. The process of claim 1 wherein said calcining is carried out at about 600° C. for a period of about 4 to about 12 hours.
 6. The process of claim 1 wherein the acidic zeolite is rho and the particulate binder is titania and/or alpha-alumina wherein the binder is present at ratio of about 50 weight % and further wherein the catalyst composition is modified by treatment with tetraethylorthosilicate. 